My car overheats when I’m stick in really terrible traffic, like move half a mile in half an hour traffic. It drives fine the rest of the time. I caught it and pulled over before it got too hot last time, but about six months ago it went all the way into the red zone and turned itself off (I wasn’t paying attention and it happened fast), and I took it to a shop where they replaced the fan belt. Then it drove fine with no overheating to speak of until the next time I hit terrible traffic.
What would cause this, that it only happens in bad traffic?
Engelbert Zappho Smith
Thermostat and water pump, in order of expense.
J.A.F. Rusty Shackleford
What type of car is it and how old? If it overheats in terrible traffic than your car is too reliant on air to cool the engine. Perhaps you have a problem with your coolant?
neill
thermostat
Cris (without an H)
I don’t know what causes it, but Hal Linden once told me on the teevee that when your car is overheating, try turning on the heater. It’s not comfy when it’s summer, but it draws a little heat away from the engine.
It must work, it was on teevee!
taylormattd
I would think if there was a coolant leak, his car would be overheating more than just when it is idling.
But I should shut up, I have zero idea what I’m talking about.
madmatt
That is usually caused by an old/stuck thermostat between radiator and engine block.
johnsmith1882
Sounds like you need a new Johnson Rod. It would help if you said what make of car you drive, but without that, let’s say radiator.
mikefromArlington
My first guess would be the thermostat. I believe you can disconnect a thermostat and the coolant would continue to flow regardless of the engine heat. If this doesn’t work then I believe you can rule out the thermostat and then move onto a more laborious and costly task of trying to flush out debris that might be clogging your coolant lines. Last option would be a faulty water pump.
That’s just my humble opinion….
I’d like to hear others.
Georgia Pig
Water pump or leaking head gasket.
Pangloss
Al Gore.
Tom Johnson
I think it’s that damned Obama. I bet when Bush was President, you didn’t have that problem.
tokyokie
Turning on the heater would help some, but that would address the sympton, not the underlying problem.
The Moar You Know
Lack of airflow is the fundamental cause.
Replacing the fan belt was an utterly pointless exercise.
Got to agree with neill above.
Fluckebucket
Ditto on the thermostat.
Doug Harlan J
@J.A.F. Rusty Shackleford:
The car is very old, it’s a 1998.
Mr. Cactus
Physics. Specifically, thermodynamics.
Sounds like some part of the system that’s supposed to be keeping your engine cool enough to operate properly is borked. At speed, you get enough air blowing over it and cooling it off that it’s able to soldier on anyway. Remove that airflow, and … you’ve seen the results.
I don’t know cars well enough to be more specific than that, sorry.
anticontrarian
What they said: thermostat. On the plus side, it’s a two dollar part.
Parallel 5ths (Jewish Steel)
Thermostat. Or insufficient faith. Possibly both.
Politically Lost
Most likely the water pump has deteriorated to a point where it works ok in normal driving, but can’t deal with heavy, stop and go traffic. If it were the thermostat, generally, it would just overheat. Depending on the car you may have an electric fan that is malfunctioning too.
mistermix
@Georgia Pig: The water pump thing happened to me, with symptoms similar to DougJ’s. Or at least that’s what the mechanic said, but I just junked that car because it was worn out.
Also check to see that your coolant level is not low because of a slow leak. That’s happened to me, too.
A stuck thermostat would overheat all the time, not just very rarely in heavy traffic, wouldn’t it?
Yutsano
@The Moar You Know: Yeah my first instinct was thermostat as well, considering I’ve replaced a few in my day. Fortunately pretty cheap and relatively easy to do. No mechanic should charge you more than $100 for it, and most of that will be labor.
Han's Solo
Thermostat. But I’m no mechanic.
Might I suggest the timeless, uncompromisable, almost always correct resource of Car Talk? Give them a call on Saturday, I’ll be listening. They are the source of all my car knowledge; though that isn’t saying much.
hsquared
Perhaps a problem with the radiator fan?
Ivan Ivanovich Renko
Check the radiator level next time its cold. Had that problem with my old Jeep- a pinhole leak in the radiator that caused no problems, then only caused problems when i was stuck in traffic, and then overheated regularly. I finally looked in the radiator (not the overflow tank, which was in fine shape) and discovered it was nearly dry. Put a full gallon of 50/50 pre-mix in it and it ran fine ’til I could get it fixed.
joeyess
thermostat, water pump, timing belt. check them all. go to a reputable mechanic because timing belts are expensive.
CS
I had this problem at one point. Turns out the radiator fan wasn’t coming on until the engine was too hot, and even then the fan was blowing too slowly and not moving enough air over the radiator to adequately cool off the liquid inside.
This might be a problem all the time, but driving the car is moving enough air over the engine and radiator to compensate for the reduced air flow from the radiator fan.
So, things to check:
1) The fan itself – start the engine with the hood up and make sure the fan is turning at all. Let the engine heat up and see if the fan comes on, and how fast.
2) The fan connection – is it plugged in? Any corrosion on the contacts?
3) The coolant level
4) The thermostat that controls the fan – this went bad in my car one time, too, and caused a similar problem. I might even put this as the first thing to check.
If you absolutely have to, you can roll down your windows and crank the heater up to full. That will take some of the heat off the engine. It’s not pleasant, but it did work for me until I could get the thermostat fixed.
Ivan Ivanovich Renko
PS- My old Jeep is a ’99 Cherokee, fwiw.
Just Some Fuckhead
DougJ, I’ve forwarded you an email on why you should be bicycling to work.
shep
If you’re not losing coolant, it’s probably the thermostat or, possibly, the sensor that turns on your fan. Less probable, a partial blockage of the cooling system, either in the radiator or engine block. Try having the system flushed and filled with fresh coolant and, if that doesn’t work, have the sensor checked and then the thermostat.
artem1s
@Doug Harlan J:
If its not the thermostat, the radiator is probably filled with gunk. If you are lucky it can be flushed. If you are unlucky, flushing will take away all of the gunk that was stopping up the holes. I predict a new radiator will be necessary as well as thermostat.
I love click and clack
cbear
I blame Obama for bailing out the auto industry.
Q
@Ivan Ivanovich Renko: Yeah. Had a similar situation and they found a crack in my radiator. If your levels are fine then it’s probably something else.
Surly Duff
@Pangloss:
…and his fatness.
Linnaeus
It could be a number of things:
1. Improperly working fan (NOT the same thing as bad fan belt).
2. Problems with coolant (a 50-50 mixture of water to coolant is the usual ratio, AFAIK)
3. Improperly working thermostat (this would be my first guess)
4. Improperly working water pump.
If you experience this again in traffic, and you can’t pull over, turn off your A/C (if it’s running) and turn on your heater full blast. I know that this can be uncomfortable, especially if you’re driving in hot weather, but it could help save your engine. Extended overheated or repeated cycles of overheating & cooldown can damage hoses and gaskets on your car, especially the head gasket. And you really, really don’t want to deal with that problem.
PeakVT
Your car actually has a fan belt? How old is it, anyway?
debit
What everyone else has said about the thermostat and/or water pump. Might want to have your mechanic check the oil too, make sure when you overheated last time you didn’t crack your head gasket or warp the head, as that could cause coolant to get into the oil, which would be bad.
Edited for typo.
kth
@mistermix: no, it would be functionally air-cooled while driving at normal speed, but would overheat while idling.
cbear
@johnsmith1882:
I think that’s rather dickish of you to question DougJ’s virility just because his car is overheating.
Cathy W
When this happened to me, the underlying cause turned out to be the alternator not generating enough… not sure whether it was voltage or current… to run the fan at full speed. When the car was moving faster than about 25 mph, it got enough airflow from its own velocity to compensate, but driving in traffic wasn’t good for it.
Skip Schloss
We need to know if you have an electric fan or an engine-driven fan. If electric it’s likely that either the fan itself is defective or the temperature sensor is defective. The temp sensor tells the fan when it’s time to turn on.
If engine driven, we need to know if there is a viscous coupler on the fan. This is a “clutch” sort of device that allows the fan to free-wheel at higher speeds, to prevent power loss. If the coupler is bad, the fan might not be engaging at lower speeds, (in traffic) hence airflow through the radiator is reduced.
susan
This kind of reminds me of Sully’s View From Your Window contest.
Will there be a prize for the person who correctly identifies the problem? (The Winner!)
Will Doug let us know who The Winner is?
Such excitment at Cole’s place!
Poopyman
@PeakVT: Yeah, a fan belt used to cost about $2. Now they’re called serpentine belts and will set you back about $35.
Oh. Go with the thermostat first, as it’s cheapest and easiest. Coolant flush will cost, but your car probably needs it. Check coolant level before you do anything, and do it first thing in the AM. All this is a rehash of the above, of course.
Just Some Fuckhead
@cbear:
If he was virile, he’d be driving a truck like me. And we could have matching license plates and wear cowboy hats with a feather.
negative 1
Have had the same problem twice – it was the thermostat once and the fan (not the fan belt) the other time. Both are involved with the fan that blows over the radiator when there is no airflow (i.e. when you are stuck in traffic as opposed to moving) from another source cooling the radiator itself. I was young and broke (hence motivated) at the time but it forced me to do it myself – not a difficult repair and neither time did it take too long.
Agree with everyone on the heater trick – basically your heater acts as a supplementary radiator and by turning on the heat your are turning on a little fan. Plus, it is like punishing yourself and will force you to get the problem fixed post haste.
Remember, tho… knowing is half the battle.
Just Some Fuckhead
@susan: I already know the answer but I was gonna let him spend a bunch of money on new parts before telling him to stop following the car in front of him so closely.
Poopyman
@Cathy W: Good point. You jogged my memories of having a fan go bad on my old Subaru. Which highlights the importance of Doug giving us the make, model, and year of his ride.
Dan
Doug,
To me, that sounds like what I refer to as “car trouble.” A lot of cars have car trouble, including newer models. What you’re going to want to do is first, find out what the car trouble is. What is causing it to overheat? Then second, fix the car trouble. That should clear up all of your overheating issues.
If this doesn’t work, you may have to take your car to a mechanic.
Yours truly,
Car Dude
Roger Moore
@mistermix:
This. I had a problem similar to this- overheating in heavy traffic- and it turned out to be low coolant. The advantage is that it’s a really easy problem to check and to fix.
Nate
I do not know where you live, but if its the fan itself then you should notice that it begins to overheat in less traffic and more quickly as external temps go up. You can see the fans spinning in most cars, so just turn it on, let it idle and see if its spinning.
SiubhanDuinne
Is it making a funny noise?
Huggy Bear
Extreme patriotism, just like Newt Gingrich. I’m assuming it’s a “rill Merkin” car, so when it just sits there idle, it has nothing to do but focus on how much it loves the country, and since it can’t just get up and start humping the pink 2011 Ford Catholic Schoolgirl sitting next to you in traffic, it overheats. The only way to fix this is to set up a series of sham businesses that funnel money directly to your car for essentially doing nothing but blowing exhaust.
Yutsano
@Just Some Fuckhead:
I was intrigued until the feather part. Then you just had to go all Dubya on me didn’t you?
kd bart
@johnsmith1882
That’s George Costanza’s prognosis too.
RobertB
I vote with Shep – most likely the sensor that turns on the electric fan for the radiator is bad. I would think that if it was a bad thermostat, “stuck in traffic” wouldn’t make a difference. Could be that the electric fan itself is bad as well.
kevin
If it’s your water pump, go ahead and replace your timing belt at the same time. You’ll save money in the long run because of the labor. It’s a simple job to replace the timing belt when you’re working on the water pump. If you wait, you’ll just be paying for that same labor all over again.
Mark B
Try a coolant system flush, followed by new coolant. If someone has used tap water, the calcium can collect in the radiator, reducing the efficiency of heat exchange.
If your car has a fan clutch, I’d recommend replacing that, too. Maybe a heavy duty fan instead of the stock one. If the radiator is in good condition, it probably has to do with air flow, since it’s fine when you’re going and the movement of the car is pushing air through the radiator.
It might also be something as simple as ignition timing, which a tuneup could fix.
Edit: duh, electric fan, probably. You should hear it come on when the car gets above normal temp. If you don’t it’s probably the fan switch or the fan motor.
khead
It’s all ball bearings nowadays. Now you prepare that Fetzer valve with some 3-in-1 oil and some gauze pads. And I’m gonna need ’bout ten quarts of anti-freeze, preferably Prestone. No, no make that Quaker State.
Just Some Fuckhead
@Yutsano:
That doesn’t seem rakish to you?
Georgia Pig
I doubt it’s the thermostat, but that’s easy to check, just remove it. The fact that it occurs in traffic makes me suspect a water pump because you’re running at or near idle with no breeze through the radiator. A pump running at less than nominal capacity might provide sufficient coolant flow at speed, but not at idle. Alternatively, the head gasket could have a leak such that exhaust gases are getting in the coolant. This foams up the coolant and makes heat transfer less efficient. This is exacerbated when you’re not moving air across the radiator. You could also have a slow leak, so check your coolant level, but I would think they might have checked that when they replaced your fan belt.
Paul Gottlieb
After years of listening to “Car Talk” I feel confident in saying the problem is with the Crank Angle Sensor! But seriously, the reason it only overheats in bad traffic is because as long as you’re moving, the air flow over the radiator is enough to prevent overheating. The fan is only essential when you’re stopped or very slow in stop-and-go traffic. If may be that the sensor that tells your cooling fan to turn on isn’t working, or the fan itself is defective
taylormattd
@Dan: Ha.
Yutsano
@Just Some Fuckhead: It seems…something. I don’t recommend trying that in Wyoming however.
Although there might be a pheasant feather exception. Especially if you durn shot the critter.
alhutch
Doug – If you don’t know the last time your car’s coolant was flushed, you probably need it. Figure coolant flush, new thermostat and water pump (in that order) as possible fixes for your issue. Flush and thermostat should be done together. Water pump might be more involved, depending on your car.
Your car’s mileage will also dictate the need for these services (i.e. water pumps are a wear item, coolant should be flushed per factory service schedule).
susan
Have you tried burping your radiator? If that doesn’t work, flush it! (Not the whole car, just the radiator.)
(I know nothing about cars, but I did stay at a Holiday Inn last night.)
Just Some Fuckhead
@Yutsano:
Jaunty?
mrami
Thermostat and/or clogged radiator. When this has happened to me, it was a clogged radiator (’83 Tercel).
Yutsano
@Just Some Fuckhead: Uhh…sure!
(the power of positive reinforcement. It’s not just for breakfast anymore.)
Elisabeth
@Doug Harlan J:
I’m late to this party but my car does, and always has done, the same thing. It’s a 1997 and simply hates to sit in traffic. I always turned the air on, silly me. Guess I’ll try the heater next time.
fhtagn
It’s because of all those traffic moochers stealing highway space from the producers. You need to do the honorable thing and go Galt. Just watch the economy collapse! I promise, the moochers will be eating each other and demanding your return by … well, roughly May 15th. At least,that’s the best estimate Reason has available at this point.
Just Some Fuckhead
@Yutsano: At the very least, natty?
attica
Yeah, it’s the fan sensor. I have the same problem. I only overheat in stop & go traffic, and even in cold weather.
Interestingly, I save the day by turning the AC on, not the heater. That forces the fan to operate, and I’m back in the green zone within a minute.
Just Some Fuckhead
@Elisabeth:
Duh, this lets all the cold air out of the engine.
Doug Harlan J
@PeakVT:
Sorry, I mean fan, not fan belt. I don’t know why I wrote fan belt.
dave
With the engine at operating temperature if it was the thermostat it would overheat at every red light it wouldn’t take half an hour.
check the coolant level preferably in the radiator not the overflow tank and while you have the cap off start the car and see if you have circulation once engine is warm (rough check of the water pump and thermostat)
if it has an electric fan motor (and not a fan belt) see if the fan starts when the engine is at operating temperature if not replace the fan sensor.
So if there’s enough coolant and there is circulation and the fan does run you will most likely need a new radiator, you can try to flush it but at that age it will probably not clean out enough or it will leak.
geg6
@Georgia Pig:
I agree with water pump. My old car did this all the time until I finally had the damn pump replaced.
Doug Harlan J
I’m thinking it is the fan sensor, maybe. And if I just turn on the A/C that will force it on? Will turning on the heat force it on too?
PeakVT
@Poopyman: V-belt, serpentine belt – either way, not many new cars have fans that are actually run off of a belt.
@Doug Harlan J: Ok, that makes more sense.
susan
If you can get her to Denver, my car mechanic, Leo, will fix’er up as good as new!
If you don’t want Leo, my son-in-law’s a mechanical engineer; he’s good at taking things apart, but getting them back together again is another story!
He’s cheap tho….
goblue72
Speaking of Car Talk, you really need to ask them this question on their next show and list all the answers you got when you posted the question “on the Internets.” Between that and your snark abilities, its a guaranteed 15 minutes of pure radio comedy gold.
Tsulagi
Going to go way out on a limb and assume you’ve checked your coolant level. And actually added if needed.
Going to go against the thermostat consensus. Yeah, it’s often the overheating culprit, and the cheapest fix. But almost always thermostats either work or they don’t; there’s no middle ground where they sometimes work. If your thermostat was stuck closed, you should be overheating in all conditions. If it were stuck open, you shouldn’t be overheating in slow traffic if the rest of your cooling system is working properly.
Also don’t think it’s the water pump. When they go, they tend to go quickly. When the bearings start wearing out causing play in the shaft, their wear accelerates real fast to the point the pump will seize. Often you’ll hear metal on metal screeching sounds from it before it fully locks up. Sometimes the impeller will lose a fin or two reducing its capacity, but not very often.
Given your symptoms, I’m gonna go with radiator. Sounds like your thermostat and water pump are working, but when you’re not getting enough air circulation, you’re also not getting enough water circulation when idling in slow traffic. Could be scale or rust clogging the radiator passages. Have you ever flushed your radiator? Changed the antifreeze (it’s a rust inhibitor too) every couple of years and all those other good maintenance kind of things? If not, here’s where you are.
Fucen Pneumatic Fuck Wrench Tarmal
remove the terrestrial radio. its the ire of a thousand limbaughs, concentrated in the airwaves like magnifying glass to an ant, the giving you the hell fire you deserve.
Halteclere
Doug,
1) let your car idle in your driveway to see if it gets hot – but don’t let it overheat. While it is idling observe the fan to see if it turns on and pulls air through the radiator. If the fan does not turn on then you have a clutch / fan sensor issue (I don’t know what these new-fangled vehicles use).
2) If your fan turns on, or while it is getting hot, see if your radiator becomes hot to the touch, and if the air that your fan pulls through your radiator becomes hot. If neither happens then your coolant is not properly circulating (but this would probably cause you to overheat even during normal driving).
I doubt the problem is with the thermostat, If the thermostat is sticking in any position except fully open then you will have overheating anytime you drive your car at any speed. If your thermostat is sticking open your car will take a lot longer to heat up than normal. Removing a thermostat may actually make the problem worse, for (at least several years ago) thermostats regulated the flow of the coolant, allowing coolant to remain in the radiator for a longer time, which allowed the coolant to cool further.
I also doubt the problem is with the water pump, for poor circulation will cause overheating for all types of driving.
Has anyone done any work on your car in the area of the radiator / fan? If a sloppy mechanic removed the fan shroud and didn’t replace it, you would have a condition where the air circulated around the fan blades and the fan drew less air through the radiator. This would definitely affect cooling when you were stopped compared to when you were driving.
Has your radiator or AC condenser become clogged with junk? Check to see if the fins are all open and not obstructed.
Finally, check your radiator hoses to ensure that they are not collapsing from the suction of the water pump. Older hoses may lose their strength and the hose under suction will collapse (or partially collapse) and will restrict coolant flow.
Disclaimer: For 18 of my 24 years of legal driving I’ve only driving (and did all the work on) cars built in the ’60’s, and have lots of overheating experience.
Tsulagi
@Doug Harlan J: Easy way to check whether the fan and its sensor are working. Start your car in your driveway with the hood open. Let the car warm up. When it gets hot, as in your stop and go traffic, the fan should kick on. If it doesn’t, either the fan motor or its heat sensor isn’t working.
elspi
I am going to go with radiator. You probably need to have it rodded.
Don’t use your own Johnson though ;-) This is best left to the professionals.
RGuy
@Cris (without an H): Actually it really does work.
attica
I don’t get relief turning the heat on; only turning on the a/c has ever worked (on this car/for this problem).
Last time I took it to a mechanic, they replaced the water pump for $600 bucks, and I had a repeat of the issue not a month later. I mean to get around to fixing the sensor one of these days, but I might get rid of the car first. Mine’s a 2000, for what it’s worth.
Ukko
@johnsmith1882: If it is not the Johnson Rod it might be the muffler bearings. You should have those checked as well since they can have all sorts of unrelated sounding symptoms.
stickler
Without knowing what the hell kind of car this is, giving advice is utterly pointless. Your problem could mean one thing in an F150 with a V8 and something else entirely in an Audi with the straight-5.
Japanese, American, Korean, German? 65,000 miles or 475,000? Good maintenance records, or “meh, it’s making a sound”?
Oh — and what color is it?
Lee
I concur on changing the thermostat. This is a job that is really simple to do yourself.
The ‘turning on the heater’ thing actually works. I drove a ’83 landcruiser for 21 years and over 300k miles.
Cleaning out the radiator of gunk is probably not a bad idea either.
Jamey: Bike Commuter of the Gods
Pray tell, what is GOOD traffic?
trollhattan
A car with a fan belt? Made in the last twenty years? I suspect you’ll need new muffler bearings and smoke generator.
RossInDetroit
The car hates your freedoms. And it hates your way of life.
p.a.
If you have a thermostatic-controlled fan that’s a trouble spot.
With the motor COLD open the radiator cap and start the car (if radiator isn’t full fill with 50/50 then start). When engine warms the coolant level should decrease, as the thermostat opens to allow coolant into the engine. If coolant doesn’t draw down, thermostat problem, possibly crappy, blocked radiator problem. If your radiator looks crappy on the outside it’s probably crappy on the inside, without necessarily leaking. And for god’s sake if you’re flushing/refilling the radiator replace the thermostat also.
My experience with waterpumps is they go all at once, not slowly, so having problems when in stop and go traffic isn’t something I’d associate with them.
Nemesis
Check the diframaloid.
fhtagn
@RossInDetroit:
You know, if DougJ would only union-bust those hamsters he’s got under the hood, he’d be just fine. But will he listen to sensible real American advice? No, sir, he will not! The man is defiant and unreasonable. Frankly, I fear we may have to taze him to get him to see sense.
Halteclere
A couple more thoughts:
A degraded water pump could cause this issue, if it is the kind of pump with plastic or cheap metal blades. If the blades wear over time the effectiveness of the pump decreases. Sitting in traffic the car will be turning slower RPMs and the pump will not pull as much water as when the engine is turning faster.
If you get stuck in traffic again try increasing the RMPs of the engine (burning more gas sucks, but destroying an engine sucks more). Coolant will circulate faster through your engine, and your fan will pull more air through your radiator.
Turning on a heater will always remove heat from the coolant system. If the issue is a bad fan sensor, turning on the AC may (depending on the car) automatically override the fan sensor and turn on the fan / engage the fan clutch.
Depending on how often you get in really bad traffic, your car could have had this condition for a very long time before you noticed the issue.
Jon H
Thermostat.
dmbeaster
I vote thermostat, even though it is a little weird for it to fail intermittently (only with heavy stop and go). I have had this same problem caused by a thermostat (on a Ford Explorer). It is as if it has only partially failed. They more typically fail completely and you cant get any decent cooling.
But all of the other suggestions are candidates.
ChrisNBama
It’s an airflow problem. When the car is moving freely, lots of forced air enters through the radiator cooling things down. When you are idle, or nearly idle, you do not have sufficient forced airflow and overheat.
I had a similar problem and had to replace the thermostat and threw in a new radiator as well (to be safe). Works fine now.
mattski
not sure on your make or model of car. but the problem is with the radiator fan not spinning or spinning fast enough. When driving you are pushing enough air through the radiator to cool the coolant. However in stand still traffic no air is going across the radiator.
Pop the hood of your car, start your engine walk back to the front of your car and see if the radiator fan spins.
Not sure what powers your radiator fan. But if you follow the fan belt it should run through some pullies and tensioners that go bad over time, the fan belt should then connect a fan clutch that connects to the water pump. Without the car on, see if the fan belt is tight.
Inspect the both sides of the belt your mechanic said he replaced and looks for small crack in it. If there are then your mechanic lied to you and never changed the belt.
anyway those are the things I learned when my radiator fan blew up like a grenade and took out my radiator two months ago. @220k miles I replaced all those parts on my car.
Billy K
You’ve heard it already, but I’m just trying to get a kickass echo chamber going here:
1. Thermostat
2. Water Pump
3. Radiator (and/or radiator lines)
If it were anything else, I’d be very. very surprised.
Max Peck
Fan clutch.
honus
@Halteclere: what he said.
All the people talking about the thermostat and water pump have no idea what they’re talking about. If the thermostat or water pump is bad it will overheat all the time, but especially when you are driving at speed. This car probably has an electric fan which cools the radiator when the car is sitting still, and the fan or the thermal switch for this fan is bad.
If it is a belt-driven fan (not really likely) then that’s why changing and tightening the fan belt helped before.
My 2¢ as a somebody who began rebuilding truck engines when I was 12 (that would be 1967)
Danton
Same thing happened to my Lamborghini. I just traded it in for a Ferrari.
Lynn Dee
When you’re speeding along, your engine is cooled by the air flow; when you’re stuck in one place, it’s not. So it’s not surprising that you’re seeing this only when you’re stuck in traffic. But you do need to get the problem fixed. And turning on the heat when the car is overheating does help, since heat is vented off the engine into the interior of the car.
dmbeaster
honus – I have had this exact problem with a faulty thermostat – car only overheated in heavy stop and go traffic. Yes, when they fail, you typically get overheating period without regard to driving conditions, but not always.
ump902a
If it has one, I’d say the fan clutch.
RossInDetroit
Whatever you do, don’t ignore the temp gauge. I made my wife write the check for her new engine so she would remember not to drive ‘just a little farther’ with the needle pegged in the red.
honus
@dmbeaster: I’m not necessarily disagreeing, but I have never seen a thermostat fail that way in over 40 years of fixing cars. Even if a thermostat is partially failing, the overheating will be more severe at speed because the engine generates so much more heat when it’s working. Again, anything can happen, but i’ve never seen a thermostat that closed up as it got hotter.
Turning on the heater helps some simply because the heater is actually another small radiator inside the car. It’s like a having a slightly bigger radiator, but this tactic won’t work in the long run.
Clogged radiators, bad water pumps, etc. could cause overheating at idle, but generally the car will also overheat at speed. And these are more expensive to fix. The fan cools the engine when the car is sitting still, and if the car overheats when it is sitting still, this is the first thing I would check. It’s easy to check and relatively easy to fix. If the fan is working properly, then you could look at those other items, but until the fan is checked out, all the other items are just expensive guesswork.
YellowDog
When you say fan belt, is it really a fan belt running the fan? Most cars now have electric fans that are controlled by a thermoswitch on the radiator. When you’re driving, the airflow will cool the radiator and the fan does not run. When you are stopped and the radiator begins to increase in temperature, the fan will turn on. If the thermoswitch is faulty, you overheat at stops. This is the likely source of your problem. If it were a bad water pump, your engine would be a glowing mound underneath the hood. If it were the timing belt, you would be stuck at the intersection until the tow truck arrived.
Bill H.
If you have a fan belt it is not thermostatically controlled fan, so that is not the problem. If it’s a 1998 it has almost certainly not got a clutch. The thermostat is unlikely as hell, it would overheat more often. The symptom is that high speed is forcing more air through the radiator, low speed is not. That spells radiator issue. It may be a buildup of crud on the outside of the radiator. It may be buildup inside. Drain and flush. That will probably create leaks in the radiotor and blow out at least one hose. New radiotor is the cure for that.
Fucen Pneumatic Fuck Wrench Tarmal
@Danton:
ah, a person who is impressed by the application of a single principle. piker.
keeping a 10 year old truck and 11 year old car on the road,and reliable, requires the application of many principles.
honus
@Bill H.: lots of cars with electric cooling fans and auxiliary fans have fan belts. (many vehicles have belt driven fans supplemented with electric fans, hence “auxiliary cooling fan”)
All belt driven fans have had clutches (to save the power of driving the fan at high speed) since about 1965. (some have flexible blades which flatten at higher rpm to accomplish the same thing, but clutches are by far the most common) Even if the fan is not belt driven, most likely the water pump is. Tightening the fan belt will often help a cooling problem if the water pump is belt is slipping, and this may happen more at idle.
Check the fan and belts first.
Sad_Dem
Sitting in traffic is what places the most demand on a car’s cooling system, so it’s no surprise that the problem crops up then. If you’re moving, air moves over the radiator.
New thermostat: cheap, but unlikely to solve the problem by itself.
Radiator flush: also cheap, may fix the problem by itself
More new parts: not cheap, but more likely to fix the problem.
The first thing I’d check after a flush is the fan–is the fan clutch/switch working? Etc.
If you have the money, a new fan and radiator, plus new hoses. Otherwise work up the expense ladder.
Another possible problem is the slow leak, which has been previously described. The slow leak can also appear in the hoses/clamps.
Bob
@Billy K:
Adding one more in order of expense:
1. Add water/coolant
2. Thermostat
3. Water Pump
4. Radiator (and/or radiator lines)
greylocks
For purposes of giving advice here, the type of car really shouldn’t matter unless it lies on the extreme edges of the engine size/type/performance paradigm. All standard water-cooling systems work pretty much the same way and have for a gazillion decades or so.
If there are no other symptoms than the one described (overheating at idle), the prime suspects are
(a) the radiator fan and/or its associated electronics and wiring.
(b) a clogged system
Usually neither is hugely expensive to fix. A professionally-done pressure flush will usually take care of (b). However, if (b) is bad enough, you may have to replace the radiator. If that’s the case, ask your mechanic to put in a refurbished one. There’s no reason to pay for a new radiator if a refurbished one is available.
It’s not likely the thermostat, but this is an easy and cheap part to test, so rule that in or out first.
The chances of it being the water pump are close to zero. 99 times out of 100, when a water pump goes, it goes quick and lets you know. It either springs a huge, system-draining leak, or it seizes up, or both. If it has done neither by now, it’s almost certainly not the WP. So don’t let yourself get talked into that hugely expensive repair unless everything else has been definitively ruled out.
Tsulagi
@honus:
Me too. But in an earlier comment DougJ said a shop replaced his fan, not fan belt as in his post, six months ago. Assuming the shop didn’t take him for a ride simply washing or spray painting his old non-working fan while correctly believing their customer wouldn’t be smart enough to check in their driveway whether it works or not when the car heats up while idling, I’m going with it’s likely working. Agree given his symptoms and length of time he’s had them, probably not thermostat or water pump.
I’m still going with radiator. Know a lot of people who never flush their radiator or change antifreeze.
SiubhanDuinne
@Bob:
Oooh, looks like a fun game!
jon
If it’s a Japanese car and you’re somewhere it gets quite hot, the overheating might be related to the radiator being something designed for a Japanese climate. You might want to look into a double-walled radiator.
But most likely it’s that thermostat or the fluid levels. Or the pump. Or you just suck at choosing your route. Or you blast the AC too much. Or something else that blames you rather than your car. Are you too fat? Just asking.
twiffer
over 100 replies, and not one link to tmbg’s thermostat?
for shame people.
MFA
Depends. Is the battery a 6- or 12 volt? ;-)
Danton
@Fucen Pneumatic Fuck Wrench Tarmal: I actually drive a 15-year old Ford truck.
Don K
I blame gay marriage.
milo
Before you troubleshoot the follwing: thermostat, fan sensor(temp switch?), fan motor, etc. — do yourself a favor and check the fuses first.
BruceJ
Our old honda had that problem, turns out that they had three different grades of thermostat, and idiot father-in-law (previous owner of the vehicle in question) had gone for the ‘Lives near the arctic circle’ one.
Swapped in a t-stat set to open at the low end and all was just fine…never had another lick of problem with the thing overheating in traffic.
I had to block half the radiator to get it to warm up in the winter, but that was an easy ‘piece of cardboard’ fix.
EIGRP
Where do you hit bad traffic in Rochester that would make you stand still for more than 5 minutes?
Even driving to the east side from downtown at rush hour, I am never delayed more than 5 minutes getting home.
OTOH, the construction season does seem to make people drive 25 in a 55MPH zone….grrrr…
Also – make sure your radiator is full.
Eric
Ajay
I have 1999 Chevy Venture and it has had the same problem for few months. For me, its the coolant which leaks and doesnt circulate to cool the engine. It may not be the case for you but check if coolant level is ok. I did drain it myself and poured all new one although that didnt help too much. I wouldnt get it flushed as it can harm the gasket. In my case, it does help to have the heat on as it forces the coolant to circulate, cooling the engine. Another issue may be the water pump. I dont trust any mechanic to spend $1000+ on it to replace the gasket. I have only 80K miles on it and I am the original owner.
Couple of days ago, I test drove Hyundai Elantra (40mpg on highway, 29 in city). I liked it. Wife doesnt want to give up Van :-( for a mid size fuel efficient car.
Ed Drone
All this talk, and no one has suggested properly inflating the tires!
And yes, I’d suspect the fan and its controller first, the thurbostan second, and the radiator third.
Ed
Brother Shotgun of Sweet Reason
If the head gasket’s blown and coolant is in the oil, the dipstick will look like it’s covered in mayonnaise.
Generally when I’ve lost a water pump it’s been catastrophic. Steam, fountains of water, shredded fan belt.
Last time I had this problem it was a cracked radiator.
BTW I’ve been using that heater trick since I learned to drive in British cars lo these many years ago.
Cain
@Han’s Solo:
I second this. It would be entertaining.. it’s something my wife loves to listen to.. she’s loves listening to a lot of the saturday npr shows.
g grahame
Check the actual fan. In many cars it only comes on at low speeds. It has happened to me in my 93 Dodge caravan. Watch your fingers in case I am wrong
gg
techno
Old car. Only overheats in bad traffic. This is obviously a radiator problem. They get old, lose their effectiveness, and eventually not even radiator flushes will bring them back to heat transfer standards. If you intend to keep this car, get a NEW radiator. Flush out the block WELL before you put it in. Take this opportunity to replace the belts and hoses because they are probably on their last legs too.
And now your car will be ready for another 100,000 miles. I got 296,000 miles on my last car doing precisely this sort of maintenance work. There is no better way to reduce your transportation costs than to learn effective, organized maintenance.
Martin Schafer
When I was driving a cab this happened every spring to all the cars (old police crown vics). The problem was cottonwood fluff and other pollen plugging up the air passages in the radiator. The solution, blowing out the gunk with compressed air.
Might be more complicated here but this is the cheapest thing to try.
Jennifer
I’d definitely check the fan first. I had the same issue last September; fortunately I was able to self-diagnose it…what happened was when I was at a stop, the a/c would start blowing warm air; then when I got moving again, it would blow cold. Turns out I have an all-purpose fan that cools both the radiator and the a/c coils. I popped open the hood, started her up and turned on the a/c full blast and…no movement in the fan. Went out to AutoZone, bought a new fan motor for about $75, and had my brother-in-law install it – took him about 5 minutes. Of course, that’s all specific to my make of car. But something to check.
MLE
I’ll second the radiator — in older cars, or any time you don’t use distilled water in the cooling system — gunk builds up. It degrades radiator performance generally until a gunk comes apart and starts blocking the channels. If it were a thermostat or fan or other such problem, it would likely manifest itself fairly quickly in stop and go traffic. Getting the radiator isn’t too expensive either, I got mine done after similar problems occurred a few years back for about $80 at a radiator shop; problems fixed.
Nevertheless, a thermostat is very inexpensive & simple to replace, so its always a good place to start.
Varmintito
The basic tendency to overheat in stop and go traffic has three causes: (a) the engine is probably already hot from having driven in normal traffic, (b) you are putting an intermittent load on the engine with the constant acceleration from a dead stop (when the engine is idling it burns far less gas, thereby generating less heat), and (3) you do not get the natural cooling action of air passing through the radiator at high speed.
Some cars are poorly designed and tend to overheat under these circumstances even if there is nothing “wrong.” This is probably not the case with a car as new as 1998, and is certainly not the case if your car did not overheat in stop and go previously
There are several possibilities:
1. Coolant level is too low, which may indicate a leak. Although the cooling system is designed to be semi-closed (to minimize coolant loss through evaporation), it is possible, over a long period, for the coolant levels fall too low without a detectable leak. If the level is low, you fill it, and it drops noticeably within a month, or you notice coolant under the engine compartment, you have a leak. (you need to check levels cold both times or hot both times to account for thermal expansion). If adding coolant fixes the problem and it stays fixed long term, celebrate your good fortune.
2. The thermostat might be stuck. The thermostat is a bimetallic valve made from two types of metal with different coefficients of heat expansion. It is designed to prevent circulation of coolant until the engine heats the coolant to about 190 degrees, at which point the heat causes the two types of metal to expand in such a manner that it permits coolant flow. Why have a thermostat at all? Because cold engines run less efficiently and with faster wear, and in winter provide no heat to the passenger compartment. In other words, ignore advice to remove and not replace the thermostat. Once the engine heats up, the thermostat opens to permit the coolant to flow through the radiator. If the thermostat is stuck or only partially opens, the coolant does not flow through the radiator.
3. The water pump might be broken. The water pump is a mechanical pump driven by an engine belt. If it seizes up, it does not circulate the coolant through the radiator. Unless the coolant circulates through the radiator, it will not lose heat.
4. The radiator might be blocked internally or externally. The heated coolant flows through the radiator, which is a series of thin metal tubes with fine metal fins. It is placed at the front of the car so air will pass between the tubes and fins at high speed, thereby cooling the coolant, which then circulates to the engine. Blockage can happen several ways. Build up of deposits in the tubes can prevent coolant flow. Kinked radiator tubes can blocked coolant flow. an over-repaired radiator will eventually lose its cooling capacity because the most common repair is to seal leaking individual tubes, thus preventing the leak but literally taking that tube out of circulation. Build up of dirt, leaves, and other crud on the tubes and fins can prevent air flow, making the cooling less effective. Finally, the fins are super thin and bend easily. they are designed to be vertical to the air flow so the air can pass through the radiator tubes and fins more easily. If too many of the fins are bent, they it impairs air flow (You’ve probably seen this on window air conditioners, where some genius decides to write his name by bending the fins with a stick, a pen, or a finger).
5. The radiator fan may not be working. All car engines have had a primary engine fan, which is driven by the engine. Its purpose is to blow air through the radiator. When the car is idling, off, or in stop and go, the primary fan might not be enough. Modern cars have a secondary radiator fan. It is electric, so it does not depend on engine RPMs to do its job. When internal engine temperature passes a certain threshold, a thermometer in the engine activates the switch on the fan.
Finally, the reason turning on the heater can cool the engine is because turning on the heater opens a valve that lets the coolant circulate through the heater core. The heater core is basically a small radiator, usually located behind the dash. When you turn on the heater, the same kind of heat exchange occurs as normally would happen with the radiator. The effect is usually pretty weak for several reasons. First, the tubes and fins of heater core have probably less than 1/4 the surface (i.e., cooling) areas of the radiator’s tubes and fins. Second, even with the heater fan at full blast, it does not even approach the cooling affect of air constantly passing through the radiator at highway speeds. Also, the heater core housing is not much larger than the heater core, which means that the air in the housing gets hot. 180 degree air does not cool engine coolant as efficiently as 100 degree air, which is about as hot as it gets most places in the US not named Phoenix or Las Vegas. This, of course, is by design. The purpose of the heater is to provide heat. And, of course, this particular works best the higher you have the heater fan. This gets miserably hot very fast. I only recommend doing this if the thermostat is redlining and you fear imminent engine failure. Once the crisis has passed, get thee to a mechanic.
Most, if not all, modern cars have a fan
Deb T
Don’t add coolant to a hot engine unless it is running – you’ll crack the block.
There are coolant over-flow tanks that are easily installed to save your coolant.
Turning the heater on will work at times if you don’t die of heat stroke.
Otherwise, all the other more sophisticated advice is worth a try.
Bill
If your car has an aluminum cylinder head, it may have warped from multiple overheats. Subarus, in particular, are prone to this. A cylinder leakdown test would give some insight into what is going on inside the engine, should the add coolant/thermostat/fan switch suggestions not work.
I could offer additional advice if I knew make and model.